Wave translation system



Aug. 27, 1935. El PETERSON 2,012,286

WAVE TRANSLATION SYSTEM Filed Jan. 29, 1932 4 Sheets-Sheet l F/G.3A g FIGJB FIG. 3c

% F SE 3 v INVENT OR 5. PETERSON ATTORNEV Au 27, 1935. E. PETERSQN 8 WAVE TRANSLATION SYSTEM Filed Jan. 29, 1932 4 Sheets-Sheet 2 FIG. 4 I 5 FIG. 6 7

INVENTUR E. PETERSON By J W2 ATTORNEY Aug. 27, 1935, EIPETERSQN 2,]l2,286

WAVE TRANSLATION SYSTEM Filed Jan. 29, 1932 4 Sheets-Sheet 3 IN [/5 N TOR E. PETERES'ON A TTOR/VEY Aug. 27, 1935. som 2,@12,286

WAVE TRANSLATION SYSTEM Filed Jan. 29, 1 2 4 Sheets-Sheet 4 INVENTOR E. PETERSON ATTORNEY Patented Aug. 27, 1935 UNITED STATES WAVE TRANSLATION, SYSTEM Eugene Peterson, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application January 29, 1932, Serial No. 589,594

22 Claims.

This invention relates to wave transmission, and has as objects distortion reduction and transmission volume control.

Other objects are to effect volume control without introducing unnecessary distortion in the transmission and to facilitate obtaining the desired range of volume control.

Automatic volume control devices or circuits may be classified according to their speed of op eration, some acting instantaneously andothers involving delay. In some cases the device may be required to operate instantaneously while in others varying amounts of delay may be tolerated, or even required. Instantaneously acting devices are usually associated with amplitude distortion, and therefore with the accompanying new frequencies, but delayed control circuits may be so arranged as to minimize modulation. By using degenerating circuits in volume control work certain advantages can be realized. In the instantaneous devices distortion can be reduced, while in the delayed devices the desired gain variations can be more easily obtained through the multiplying action of a degenerating circuit.

Other objects and aspects of the invention will be apparent from the following description and claims.

In the drawings:

Figs. 1, 2A, 2B, 20,. 3A, 3B, and 3C are diagrams for facilitating explanation of the inven tion;

2D is a limiter circuit or volume compressor embodying one form of the invention, and includes also a cross-talk reducing circuit embodying a form of the invention, and the circuit of this figure can also be adjusted to be a volume expander embodying a form of the invention, and including a volume limiter embodying a form of the invention; and

Figs. 4 to ll show schematically other forms of the invention.

Before discussing the various circuits in detail some of the properties of degenerating circuits will be noted by reference to the simplest form of degenerating circuit, the alternating current paths of which are shown in Fig. 1. Here the degenerating resistance r is common to both plate and grid circuits of an amplifier tube'i. The circuit equation is V-I-ILVBIZB where (If the generator 6 were transferred from. the

types of control hold good. When reactances are introduced in circuit, 5 becomes a complex quantity.) The grid voltage 1) is therefore less, in the case under consideration, than the applied generator E. M. F. e by the degenerating factor l/(l-t s). In order to raise the grid potential to that existing when the feed-back is removed, the generator voltage can be increased by the reciprocal of that factor. The flow of modulated products may be attributed to fictitious generators in the plate circuit, the amplitudes of which depend upon the fundamental plate current. The degenerating factor operates on these E. M. F.s so that the ratio of modulation to fundamental is correspondingly decreased. Ihus, Equation (1) applies to the fundamental and also to the distortion products so that at a definite fundamental output distortion is smaller with the dengerative circuit by the amount of the degenerating factor.

It is evident from (1) that by varying p; the grid potential may be made to vary correspondingly. The fundamental plate generator voltage E,

E-pv 1+ILB reduces to 2/6 when ,u is large, so that the output current is independent of the in this case. When 2 or [3 are functions of v the equations become non-linear and in some cases of involved form. A simple graphical construction to exhibit the relation between t and e is always possible however, when, as will be assumed, s involves no phase angle. For example, with the grid biased to negative potential below that corresponding to plate current cut-off, such as the potential at c in Fig. 2A, which shows the usual static char-- acteristic of tube I, a relation such as that given by curve A of Fig. 2B is obtained between the fundamental component of grid potential 12 and the fundamental voltage component 12,143 across the resistance r of Fig. 1. Both 12 and 13 are plotted to the same scale. Drawing the line indicated through the origin, the generator potential is given to scale by the horizontal distance" between the point on the curve A corresponding to a definite v and the 45 line so that the relation between o and e is definite. Apparently the grid voltage 12 is limited the more sharply as s is increased, approaching an asymptotic maxi: mum as p becomes infinite; for example, for curve A the values-of s are larger and for curve A'tthey are smaller than the correspond-' ing values for curve A. The 6-1) relation is plotted directly in Fig. 2C in which curves B, B, and B" correspond to curves A, A, and A", respectively, of Fig. 2B. Each of curves B, B, and B" has a linear range up to the point at which the control tube is actuated, and beyond grid and cathode of tube I and a load circuit'S' as shown in Fig. 2D. In a sense the circuit of Fig. 2D acts as a compressor, with respect to transmission from c to 3, since the gain to the fundamental is. reduced as 'the amplitude is increased. Transmitting through the tube I, however, (i. e., considering R as the load circuit) gives a device of the expander or'cross-talk re ducer type since there is a large loss at low inputs anda low loss (or a gain) at high inputs. In FigQZD Y grid' battery 5 biases the grid of tube I tothe' voltageat c in Fig. 2A. Space current for tiibeil is suppliedirom battery 6 through choke c'oil Ii. Grid bias for tube}, which may operate as an ordinary amplifier, is supplied from battery I through high resistance 8. Stopping condense rs 9' of low reactance' isolate the grids of tubes I and 2 from each other as regards direct current bias and prevent battery fifrom sending current through resistance R. Battery iii suppliesplate potential for tube 2.

The circuit of Fig. 2D can be used as a volume expander'for transmission passing from source a to load circuit 3, or as a volume limiter for transmission from source 6 to load circuit R, by employing for the circuit of tube I a static char acteristic'such as that shown in Fig. 3A (instead of that shown in Fig: 2A) and operating about the point 0' in Fig. 3A, so as to obtain a 5 characteristic'such as F of Fig. 33 instead of A of Fig; 2B; This can be done, for example, by-

operating switches ll to includeresistance H2 in the input circuit of tube I so as to produce the bend in the upper portion of the characteristic of .Fig. 3A and adjusting battery 5 to bias the grid of tube I to the voltage at c in Fig. 3A. The 6-4; relation can be obtained by the same construction as before, and is shown as curve G of Fig. 3C.

. The same sort 'of'efiects may be obtained by shownin' Fig. 4 and Fig. 5; This comes about from the" fact that the impedance across the terminals'of the circuit rises as the degeneration is" increased. From Fig. 4 in which the degen erative circuit of' tube I is connected inseries between source e and load resistance VA Thatis, the resistance B is multiplied by the factor (1+,u18) 'which'ma'y be made large (as for example by'using an amplifier'in the feed-back path). Thus, with the degenerative characteristic'of'Fig. 2Bthe'series connection of Fig. 4 gives us a compressor or a'limi-ter, while with-that of Fig. 3B; the series connection gives us an" eX--' mainder of the circuit, as regards change of gain with level. In Figs. 4 and 5, and also in Figs. 6 to 9 about to be described, the requisite means for supplying cathode energizing current, steady grid biasing voltage and unidirectional space current have been omitted to simplify the disclosure, as they can readily be supplied in the general manner indicated in Fig. 2D or in usual and obvious manner by those skilled in the art.

The circuits so far described are instantaneously acting circuits in. which the degenerative circuit offers the advantage of minimizing distortion in the process of volume control. Where time delays are permissible or required the degenerative circuit may be applied to provide an efi'ective'amplification of the'variable resistance used to regulate transmission, for example as shown in Figs. 6, '7, 8, and 9. Fig. 6 shows tube 2' connected in a degenerative circuit which is like that of Fig. 5 and which is similarly used as a plifier-rectifier 35 to render the grid bias of tube I less negative, and consequently causes further increase of 8 and of the amount of degeneration and of the shunt resistance; and by this further increase of the shunt resistance the volume expaneling or cross-talk reducing eifect is increased.

With the degenerative characteristic of Fig; 3B the shunt connection of Fig. 5 and of Fig. 6 gives a volume compressor or limiter, (i. e. as 2 increases, ,ufi decreases and the amount of degeneration and the shunt resistance decrease): and in Fig. 6, increase of e moreover causes amplifier-rectifier 35 to render thegrid bias of tube I less negative, and consequently causes further decrease of e and of the amount of degeneration and of the shunt resistance; and bythis further decrease of the shunt resistance the volume comi In Fig. '7 transmission from source or input circuit e passes through tube I to load circuit 39. The tube is connected for degeneration, resistance 40 across the grid and filament being shunted by the path through resistance Q! and source 6 in series so that the resistance 4! is common: to the input circuit extending from the filament through resistance 4t and source (2 to the grid and-the plate circuit extending from the filament through resistance M, output side of amplifier-rectifier 35 and plate-filament space path of tube I Resistance ll corresponds to resistance r of Fig. 1 in being common to an input circuit and an output circuit of the tube I so as to cause degenerative feed-back. In Fig. 7, amplifier-rectifier 35 which, as noted above, involves the desired delay, effects volume control by changing the resistance (of the last tube of the amplifier-rectifier) in the feed-back path.

Transmission from c to circuit 30 in Fig. 7' corresponds to transmission from e to circuit R in Fig. 2D, andthe remarks above as tothat transdelay arising in the action of the amplifier-rec.-.

tifier.

In Figs. 8 and 9, tube 1 is connected in a degenerative circuit, resistance 45being common to the input and plate circuits of thetube, and the voltage across the grid and filament of the tube is applied across the grid and filament of main line amplifier 2, as in Fig. 2D.

In Fig. 8, volume control of the transmission.

passing from source e to load circuit 30 is obtained by having amplifier-rectifier 35 change the 7 grid bias on the control tube I in the same man-.

ner as in Fig. 6; and in Fig. 9, volumecontrol of transmission passing from source e to load circuit 36 is obtained as in Fig. '7 by having amplifierre'ctifier 35 change the resistance (of the last tube of the amplifier-rectifier) in the feed-back path.

That is, in Fig. 9 the resistance of the last tube. of the amplifier-rectifier is a function of the input amplitude, and this variable resistance is in series with the feedback path and so changes the. 1 amount of feed-back; whereas in Fig. 8 the am-- plifier-rectifier provides a variable bias on the grid of the first tube shown, which causes the resistance of the first tube to change'and so.

modifies the feed-back. Thus, the same kind of effect is involved in both figures, although the mechanism is somewhat difierent.

'The transmissions from e to circuit 30 in Figs. 8 and 9 correspond to-transmission from e to circuit 5 in Fig. 2D, and the remarks above as .to

that transmission in Fig. 2D apply also to these transmissions in Figs. 8 and 9, wherein, however,

there is involved the delay arising in the action of the amplifier-rectifier.

r Fig. 10 shows a part of a telephone system wherein a two-wire portion and a four-wire portion are connected by a bridge transformer -(hybrid coil) and line balancing network N in usual manner. The two-wire portion includes a telephone station or subscribers telephone set 50.

The four-wire portionincludes outgoing circuit or transmitting channel 5| and incoming circuit or receiving channel 52. These two channels may be of any desired type, as for example land lines or radio channels. It will be understood 1 that the one-way channels 5| and 52 form a link,

as'for example a wire or radio link, for connecting the two-way two-wire circuit including telephone set 5llwith a corresponding remote two way line. The remote terminal of the four-wire portion of the system maybe, for example, like the terminal shown.

In this figure, block 55 is a voltage limiter or volume compressor circuit like that of Fig. 2D, for voice waves or, other ,transmissionpassing from source 6 tocircuitfi (or in other words from telephone set5ll to line 5| in Fig. 10). Therefore, in block 55 the resistance l2 of Fig. 2D is omitted and the battery .5 is adjusted for operation of the circuit in this block as indicated by the curves 2A, 2B and described above.

Block 55 is a volume expander like that of'Fig.

2D for transmission from source e to circuit 3, (or in other words from line 52 to telephone set 553 in Fig. 10) Therefore, in block 56 the resistance l2 and battery 5 are adjusted for operation of thecircuit of this block as indicated by the curves 3A, 3B and 3C described above. The circuit of block 56 is adjusted to expand the-volume of-transmission passing from 52 to 50, for example to compensate for volumecompression produced at'tlie remote end of the four-wire portion of the system bythe voltage limiteror volume compressorcorresponding to that shown in block 55. i

Fig. 11 shows a system such as that of Fig. 10, except that the circuit of block 57. is used in place of the circuit of.block.55 of Fig. 10. In Fig. 11, resistance 'l2is' included inthe circuit of block 51 and battery 5 is adjusted for operation of the circuit of block 5'! as indicated by the curves 3A, 3B and described above. Then the circuit of thisblock is-a voltagelimiter like that of Fig. 2D for transmission passing from source e to circuit 5! (or in other words from telephone set 59 to line 5| in Fig. 11). -The expander of block 58 can then compensate for volume control produced, for example, at the remote end of the four-wire system by'a limiter corresponding to that just described-L i Systems with feed-back reducing gain, for example'for gain stabilization or distortion reduc tion, are claimed broadly in a copending application of HpS. Black, Serial No. 606,871, filed April 22, 1932, for Wave translation system, which is generic to the present application as to such subject-matter. i

What is claimed is:

1 A wave translating system comprising means for producing-feedback in said system of Waves that reduce the magnitude'of its output waves, and means for rendering the input-output characteristic of said system with feedback non-linear with respect to its operating amplitude range.

2. A wave translating system comprising means for rendering its degenerating factor small compared to unity, and means for rendering the input-output characteristic of said system with degeneration non-linear with respect to its operating amplitude range. V

3. A wave translating system comprising an electric space discharge device having anode, cathode and discharge control means, means for producing feedback in said device of waves that reduce the magnitude of its output waves, and means causings'aid control means torender the input-output characteristic of said device nonlinear with respect to its operating amplitude range.

flJA wave translatingsystem comprising an electric space discharge device, means for normally reducing space current of said device to substantially zero value,and means for produc ing feedback in said device of waves that reduce the magnitude of its output-waves below their value without feedback.

5. A wave-translating system comprising an electric space discharge device having anode cathode and discharge control means, means for normally causing said control means to reduce anode current of said device to a value approximately as'lowas zero, and means for'producing feedback in said device of waves that reduce the magnitude of its output waves below their value without feedback. l

62A wave translating system comprising an electric space discharge device having anode, cathode and grid structure, means for rendering said device degenerative and rendering its degencrating factor small compared to unity, and meansforbiasing said grid structure to a potential'that'reduces space current of said device to substantially zero value.

'7. A wave translating system comprising an electric space discharge device, means for normally reducing space current of said device to substantially zero: value; means for" producing:

feedback in said device of waves that reduce the magnitude of its output waves below their value without feedback, and means for preventing i normally causing said control means toreduce anode current of said device'to a valueapproxi mately as low as zero; means forming with saiddevice a closed feedback loop for feeding back in said device waves'thatreduce the magnitude,

of its output waves below their value without feedback, and means for preventing propagation of direct current around said'loop;

9. A wave translating system comprising an electric space discharge device, means for normally reducing space current of said device to substantially zero value, meansfor render-ingsaid device degenerative and rendering its degenerat ing factor small compared to unity; and means forpreventing' feedbackofdirect cur-rent in said: device. Y

10. A wave translating system comprising an electric space discharge device having anode, cathode'and-discharge controlmeans; means for pplying to'said control means steady negative biasing potential sufficient to reduce space current' of said device to approximately zero value, means for transmitting direct current tothe-substantial exclusionof alternating currentconnecting said cathode and anode means; other means for transmitting alternating current to the-substantial exclusion of direct current connecting said cathode and anode means; and means forfeeding back from said other means to saidcontrol means waves, to the exclusion of unidirectional voltage that reduce the magnitude of' the output waves of said device below their value without feedback;

11. A wave translating system comprisingv an electric space discharge device, a source ofinput' of the negative swing of the waves fromsaid source, and means for producing feedback insaid device ofwaves that reducethe I magnitude of its output waves below their valuewithout feedbacle 12. A wave translating system comprising an electric spacedischarge device having anode, cathode and grid structure, a source of input waves for said device,-means for rendering-- said device degenerative, and means for normally biasing said-grid structure toa potential that causes extinction of anode current of saiddevice during a considerable portion of the negative swing of the waves from said source.- i

13. A wave translatingsystem comprising an electric space discharge device having anode, cathodeand grid-means, a source of input signal waves for said device, meansforrendering said device degenerative, and means for normallybias'- ing said grid meansto such potential-as-to render anode current of said device extinct duringa considerable portion ofthe negative swing of the signal waves from said-source, said=means for rendering said devicedegenerative rendering the degenerating factor small compared to -unity for reducing;- distortion of: the signal output 14. A wave transmissionsystem comprising a wavesource, a loadam electric-space discharge device having. anode, ;cathc-de and gridstructure, with; its input and its output connected respec amazes tivelyto' said source, and said lead for trans mission through the device from the source to' the" load; means -forsupplyingto saidgrid struc ture potential for causing said device to trans-- mit portions only of the waves supplied thereto- Y from said source; andmeans'feeding back in said device waves' that reduce the distortion causedby'the transmission of portions'only of the input waves.

A- transmission volume limiter comprisinga degenerative circuit including a vacuum tube having an anode-, a cathode and a discharge control element, anoutput circuit connected across said cathode and control element, and means supplying to said control element a negative biasing potential substantially greater'than thatrequired" to reduce the anode currenttozero value.

16. A transmission volume expander comprising a degenerative circuit including a vacuumtubehaving an anode, a cathcde'and' a discharge control element, .an output circuit connected across said cathode and control element, andmeans for supplying to said control element abiasing potential of such value as tooperate said vacuum tube about a pointsubstantially midway between" the upper and the" lower knees of' its input-output characteristic;

17-. A wave transmission system comprising a- -to passage of transmission therethrough, said degenerative circuit including a vacuum tube havingv an anode, a cathode and-a discharge'controlelement, with-said resistance connected be tween said cathode and" said control element and with meansbiasing said control element to a potentiarthat normally: reduces anode current of: saidtubeto zero value; 3

19; A- volume control circuit comprising a resistance in shunt to said circuit for controllingthe'trans'missio'n efficiency of the circuit, and adegenerative circuit-including saidresistance forincreasing the impedance of-saidresistance to passage of: transmission therethrough, said degenerative circuit including a-vacuum tube having an anode,'-a cathode and a: discharge control element;- with said resistance connected between said cathode and'said controlelement and with means biasing 'said contror element to a potential that-normally redue'esanode current of said-tube to zero value;

' 20; In a'wave transmission system, a degenei-a-- t'ive circuit. for'cont'rolling the transmission efficiency of said system, means responsive to changes of transmission level for controlling operation of said'degene'rative' circuit, and means for producing delay in theiaotion" of said second mentioned means.-

21'. In awave transmission system, a resistance for controlling the transmission eificiency of the system; a degenerative circuit ineffect multiplying the value of--saidresistance,means-responsive tochanges intransmission level for varying the amount of degeneration in said degenerative circuit, and means for delaying action of said first mentioned means.

22. The combination of a wave translating device for discriminating between waves of different amplitudes by virtue of non-linearity of its input-output characteristic in its operating range, and means for rendering said device degenerative and rendering its degenerating factor small compared to unity, said device comprising a vacuum tube having means for normally reducing its space current to zero value.

EUGENE PETERSON. 

